1. FIELD OF THE INVENTION
This invention relates to a process for regenerating an etching solution for printed circuit boards to be used in telecommunication appliances, etc., decoration boards, etc.
2. BRIEF DESCRIPTION OF THE PRIOR ART
In the production of printed circuit boards, there are available etching processes for removing unnecessary copper components by use of a solution containing ferric chloride, a solution containing ammonium persulfate, etc. The process by use of a solution containing ferric chloride is directed to dissolution of copper on the basis of conversion of trivalent iron ions (Fe.sup.3+) in the solution to divalent iron ions (Fe.sup.2+), but on account of coexistence of copper ions and iron ions in the solution, it is not easy to regenerate the used etching solution. Thus, the used etching solution is discarded, or especially handled by special dealers upon request. These are the disadvantages of said prior art process.
Since the iron ions and copper ions coexsisting in the solution have different electrodeposition voltages each other, it is reported that only copper can be efficiently recovered by adjusting a voltage between two electrodes, and also generation of chlorine gas can be suppressed (Japanese Patent Publication No. 6165/71). However, it is practically difficult to recover only copper without any generation of chlorine gas, and further more chlorine gas must be blown into the used etching solution to regenerate the solution. The chlorine gas is very toxic, and has a disadvantage of giving an unfavorable influence upon human bodies from the working side as well as environmental side.
On the other hand, the etching process by use of a solution containing ammonium persulfate has been widely used since soldering plating, etc. were employed for the production of printed circuit boards, but since the dissolved copper ions exist as complex salt in the solution, it is difficult to recover it as metallic copper, and furthermore the copper ions are kept in a dissolved state in the solution, unless the used etching solution is treated in a special manner, and thus the solution is still toxic and cannot be treated in the ordinary method for waste water treatment. These are disadvantages of said prior art process.
Another process for regenerating the etching solution used in the etching has been proposed, which comprises withdrawing a portion of the solution, while diluting the remaining solution to decrease metal ion concentration and adding hydrochloric acid or hydrogen peroxide thereto regenerate the used etching solution, but the proposed process fails to provide a cyclic regeneration system, and the withdrawn solution must be treated separately. These are the disadvantages of said another prior art process.